The clock is one of the oldest human inventions, with time-keeping mechanisms, such as sun-dials and water clocks, pre-dating history. Major advancements in the precision of time-keeping occurred in the 1300s with the invention of the mechanical escapement, the 1500s with the invention of the mechanical spring-driven clock, and the 1600s with the pendulum clock.
Clocks existed significantly before clock faces or dials. The first mechanical clocks were striking clocks, designed to ring on the hour. The clock dial with an hour hand came into use in the late 1300s. The minute hand only came into widespread use around 1690, after the invention of the pendulum and anchor escapement. The direction of motion of the clock hands about the face, so-called clockwise, imitate the movement of the sundial in the northern hemisphere. The analog clock face, with an hour hand, minute hand, and twelve hours laid in a circle, has remained largely unchanged for three hundred years or more. There is a substantial preference for the simplicity and aesthetics of the analog clock face.
A mechanical clock relies on the inner mechanical spring-loaded clockwork, or a pendulum, to stabilize the period of oscillation, which is how a mechanical clock maintains accurate time. But friction robs these mechanical oscillators of a tiny bit of energy on every stroke. As the aggregate energy loss increases, the oscillations slow, leading to deteriorating accuracy for the clock. A mainspring or pendulum is designed to counterbalance this effect, continually adding stored energy to the system to keep things on track. But a mainspring or pendulum is not an infinite source of additive energy; in a mainspring clockwork, the clock must be wound periodically; in a pendulum clock, the anchor escapement has to be reset periodically. As an alternative, an electronic source can add energy to the mechanical clock.
There are also fully electronic movements, such as piezoelectric crystal oscillators, which use a piezoelectric quartz crystal to generate an electrical signal with a specific frequency, rather than rely on a series of gears and pendulums. The period of vibration for a piezoelectric crystal depends on the size and shape of the crystal. While crystal oscillators are susceptible to temperature, humidity, pressure, and vibration fluctuations, their effects are much more controllable and correctable than their mechanical counterparts.
As a result of the foregoing, modern digital clocks are much more accurate timekeepers than analog clocks attached to mechanical clockworks. Digital clock displays, typically using light-emitting diodes (“LEDs”), liquid crystal displays (“LCDs”), or thin-film transistors (“TFTs”, a variant of LCDs) have become commonplace.
In summary, the current state of time-keeping finds that digital clocks are more accurate because the analog clocks with mechanical clockworks have to account for a number of sources of inaccuracy and energy loss: friction, inertia, thermal variation, wear, and gravity, inter alia. A mechanical clock needs to be wound, or have some other source of additive energy, because the spring force eventually is exhausted overcoming energy loss. Digital clocks use crystal oscillators, or other electronic circuitry, that do not have similar inaccuracies and energy losses. As a result of the higher accuracy, digital clock displays with electronic/piezoelectric movements are supplanting the ubiquity of analog clock displays with mechanical movements. Additionally, electronic/piezoelectric movements have been mated with analog clock displays.
Although people tend to prefer the aesthetics of an analog clock display, they prefer the accuracy and ease-of-use of electronic clockworks. The main failure mode of electronic clockworks is that the power can fail, causing someone to have to reset all the electronic clocks so affected. Additionally, when mated with an analog display, an electronic clockwork can be somewhat inaccurate, due to the tolerance inherent in the angular positioning of the hour and minute hand. What is needed is a way of automatically resetting an electronic clock with an analog display, so that the analog display is always accurate.